I. Field of the Invention
The present invention relates to fiber optic systems employing multimode fibers in general and more particularly to a fiber beam compressor for use in such systems.
II. Description of the Related Art
The use of optic fibers in communication systems as a medium for transporting optical signals between locations is well known. Such communication systems generate optical signals that are carried by optic fibers to a photodetector which detects and converts the optical signals to electrical signals. The corresponding electrical signals can then be further processed by electronic circuitry.
The two types of commonly used optic fibers are single mode and multimode fibers. Although single mode fibers, which provide only one mode of propagation for optical signals have a greater signal carrying capacity than multimode fibers, the comparatively smaller core size of single mode fibers makes such fibers difficult to join or connect with like single mode fibers. Thus, use of single mode fibers is normally limited to high speed specialized applications.
Multimode fibers, on the other hand, have a relatively larger core than single mode fibers, which makes them easier to join with like fibers. The larger core is also more efficient for launching optical power therein. However, due to the hundreds of propagation modes that such fibers possess, multimode fibers suffer from intermodal dispersal and, thus, are more limited in their information carrying capacity than single mode fibers. Nevertheless, multimode fibers find many applications in certain fiber optic communication systems which do not require the highest transmission rates.
The rate of data transfer in fiber optic communication systems is limited by many factors, one of them being the photodetector which detects the transmitted optical signals. It is desirable for a photodetector, such as a p-i-n photodiode, to detect all (as opposed to a portion) of the light that is carried by the fiber. Thus, photodetectors having detection areas substantially equal to the cross-sectional areas of the cores of fibers carrying the optical signals are preferred. When multimode fibers are used, larger photodetectors are required because of the larger core sizes.
However, larger photodetectors suffer from decreased detector response time because such photodetectors possess larger intrinsic regions which correspond to longer distances across which the charged carriers have to travel for detection. Although there exist several techniques which may increase the detection rate in a fiber optic system, as for example by using a smaller detector, such techniques typically waste a portion of the photons carried by the fiber which is clearly highly undesirable.